1. Field of the Invention
This invention relates to a method and apparatus for spotting liquid samples onto dry-type frameless chemical analysis film pieces, wherein a liquid sample, such as blood or urine, is spotted onto a dry-type frameless chemical analysis film piece having a layer containing a reagent, which will undergo a chemical reaction, an immune reaction, or the like, with a specific biochemical substance contained in the liquid sample and will thereby give rise to a change in optical density. This invention particularly relates to a method and apparatus for spotting liquid samples onto dry-type frameless chemical analysis film pieces, wherein a liquid sample accommodated in a nozzle tip is discharged onto a dry-type frameless chemical analysis film piece.
2. Description of the Prior Art
Qualitative or quantitative analyses of specific chemical constituents in liquid samples are conducted for various industrial purposes. Particularly, it is very important in biochemical and clinical fields to be able to quantitatively analyze certain chemical or physical constituents in body fluids, such as blood or urine.
Recently, dry-type chemical analysis films were developed for use in systems designed for performing quantitative analyses, with which systems the amounts of specific chemical constituents or specific physical constituents contained in droplets of liquid samples spotted onto the dry-type chemical analysis films, are determined. Such dry-type chemical analysis films are disclosed in, for example, U.S. Pat. Nos. 3,992,158 and 4,292,272. It is possible to analyze liquid samples more simply and more quickly with methods in which the dry-type chemical analysis films are used than with methods in which a conventional wet-type analysis is carried out. Therefore, it is more desirable to use the dry-type chemical analysis films, particularly in medical organizations, research laboratories, or the like, where many samples must be analyzed, than to carry out the conventional wet-type analysis.
In order to use a dry-type chemical analysis film in the quantitative analysis of a chemical constituent, or the like, contained in a liquid sample, a droplet of the liquid sample is put on the dry-type chemical analysis film and is kept at a predetermined temperature (i.e. incubated) for a predetermined time in an incubator, which causes a color reaction. The dry-type chemical analysis film is then exposed to light having a wavelength, which is selected in advance. The selection of the wavelength depends on the specific biochemical substances contained in the liquid sample and the constituents of a reagent contained in the dry-type chemical analysis film. Light is thus irradiated to the dry-type chemical analysis film, and the optical density is found. The optical density depends on how much of a reaction product was formed by the reaction between the liquid sample and the reagent in the dry-type chemical analysis film. Thereafter, a calibration curve, which is created in advance and which represents the relationship between the optical densities and the concentrations of the specific biochemical substance in liquid samples, is used in order to determine the concentration of the biochemical substance in the liquid sample from the optical density, which has been found. Thereafter, the dry-type chemical analysis film, which has thus been used, is taken out of the incubator and put into a waste film box. A biochemical analysis system is constituted in this manner.
However, in general, the dry-type chemical analysis film described above is composed of a frame, which is constituted of a plastic material, and a dry-type chemical analysis film piece, which is sandwiched by the frame. The dry-type chemical analysis film piece comprises a substrate, which is constituted of a plastic material, or the like, a reagent layer containing a reagent, and a spreading layer, which layers are overlaid on the substrate. Therefore, the sizes of the accommodating section of the incubator, which accommodates the dry-type chemical analysis film and keeps its temperature at a predetermined value, a conveyance system for conveying the dry-type chemical analysis film, a supplier, which stores the dry-type chemical analysis film in the dry state before the liquid sample is supplied thereto, and a cartridge for housing the dry-type chemical analysis film, become large due to the provision of the frame on the dry-type chemical analysis film piece. Accordingly, the sizes of the incubator, the conveyance system, the supplier, and the cartridge cannot be kept small. Also, the capacity for accommodating the dry-type chemical analysis film, the capacity for conveying the dry-type chemical analysis film, and the capacity for storing the dry-type chemical analysis film become small. Therefore, the processing capacity of the biochemical analysis system cannot be kept large as a whole. Further, the cost for fitting the dry-type chemical analysis film piece to the frame cannot be kept low, and therefore the cost for the biochemical analysis cannot be kept low.
In view of the above circumstances, the applicant conducted extensive research in order to develop a technique for carrying out the biochemical analyses by using dry-type chemical analysis film pieces having no frame. For example, in European Patent Publication No. 634657A, the applicant proposed a biochemical analysis system comprising (i) a cartridge for accommodating a plurality of dry-type chemical analysis film pieces having no frame, (ii) a suction and take-out means, which may be constituted of a suction cup, or the like, and which takes each of the dry-type chemical analysis film pieces out of the cartridge such that they may not be scratched, (iii) a sample spotting means for spotting a predetermined amount of a liquid sample onto the dry-type chemical analysis film piece, which has been taken out of the cartridge by the suction and take-out means, and (iv) an incubator for keeping the dry-type chemical analysis film piece, to which the liquid sample has been spotted, at a predetermined temperature.
As the technique for spotting the liquid sample onto the dry-type chemical analysis film piece, it may be considered to directly use the technique for spotting the liquid sample onto the conventional dry-type chemical analysis film having a frame.
Specifically, for example, it may be considered to utilize the sample spotting technique, wherein a droplet of the liquid sample is formed at the bottom end of a sample spotting tip, the sample spotting tip is then moved down, and the bottom end of the sample spotting tip is thus moved to a position close to the surface of the dry-type chemical analysis film. The downward movement of the sample spotting tip is ceased when the droplet of the liquid sample comes into contact with the surface of the dry-type chemical analysis film, and the droplet is thereby spread on the surface of the dry-type chemical analysis film.
Also, it may be considered to utilize the sample spotting technique disclosed in, for example, U.S. Pat. No. 4,340,390. Specifically, the bottom end of a sample spotting tip is moved to a position at a predetermined distance d from the surface of a dry-type chemical analysis film, and thereafter a liquid sample contained in the sample spotting tip is discharged at a predetermined speed.
With the dry-type chemical analysis film provided with a frame, the flatness of the surface of the film can be kept unchanged. Therefore, even if a different dry-type chemical analysis film provided with a frame is used, the position of the surface of the film can be kept constant. However, in cases where dry-type chemical analysis film pieces having no frame are used, the degree of bending of the surface of the film surface varies for different film piece. Therefore, the position of the film surface cannot always be kept constant.
Specifically, if the conventional sample spotting techniques are applied to the dry-type chemical analysis film pieces having no frame, the distance between the bottom end of the sample spotting tip and the film surface will vary for different film piece.
If the distance between the bottom end of the sample spotting tip and the film surface becomes very large, the droplet of the liquid sample or the discharged flow of the liquid sample will break at the base portion of the droplet or the discharged flow, and part of the liquid sample will remain in the sample spotting tip without being spotted onto the dry-type chemical analysis film piece. Such problems will occur more readily in cases where the spreading speed of the liquid sample on the dry-type chemical analysis film piece is high and/or the viscosity of the liquid sample is low.
If the distance between the bottom end of the sample spotting tip and the film surface becomes very small, the level of the liquid sample being spread on the film surface will rise, and the bottom end of the sample spotting tip will become immersed in the discharged liquid sample. As a result, after the spreading of the liquid sample is finished, part of the liquid sample will cling to and remain on the outer side wall of the bottom end of the sample spotting tip. Such problems will occur more readily in cases where the spreading speed of the liquid sample on the dry-type chemical analysis film piece is low and/or the viscosity of the liquid sample is high.
A different sample spotting technique has been disclosed in, for example, U.S. Pat. No. 5,143,849. With the disclosed technique, a meniscus-like droplet of a liquid sample is formed at the bottom end of a sample spotting tip, and the sample spotting tip is then moved down. When the droplet comes into contact with the film surface, the contact is detected from a small change in the pressure inside the sample spotting tip, and the downward movement of the sample spotting tip is ceased. In this state, or after the sample spotting tip has been moved up a predetermined distance, the liquid sample is discharged from the sample spotting tip onto the film surface.
With the conventional sample spotting technique disclosed in U.S. Pat. No. 5,143,849, the distance between the bottom end of the sample spotting tip and the film surface can be controlled accurately, and therefore the problems encountered with the two conventional techniques described above do not occur. However, the size of the meniscus-like droplet of the liquid sample is small, and a comparatively long time is required to detect whether the droplet has been or has not been brought into contact with the film surface. Therefore, the speed, with which the sample spotting tip is moved down, cannot be kept high, and the sample spotting process cannot be carried out quickly.
A different sample spotting technique has also been disclosed in, for example, U.S. Pat. No. 5,133,392. With the disclosed technique, a sample spotting tip is pushed against a bottom surface of a container such that the sample spotting tip may be sealed. A pressure is applied inside the sample spotting tip, and the sample spotting tip is moved up. The separation of the sample spotting tip from the bottom surface of the container is detected by detecting that the pressure inside the sample spotting tip has become smaller than a threshold value. Thereafter, a pressure is further applied inside the sample spotting tip, the sample spotting tip is moved up, and a liquid sample is thereby discharged onto the bottom surface of the container.
With the conventional sample spotting technique disclosed in U.S. Pat. No. 5,133,392, the distance between the bottom end of the sample spotting tip and the bottom surface of the container can be controlled accurately. Therefore, the problems encountered with the two conventional techniques described above do not occur. However, the speed, with which the sample spotting tip is moved up, must be kept low such that the separation of the sample spotting tip from the bottom surface of the container can be detected. Therefore, the sample spotting process cannot be carried out quickly.